Telephone system



Feb. 16, 1937. c KOECHLING 2,071,075

TELEPHONE SYSTEM Filed July 20, 1955 5 Sheets-Sheet 1 //v WIN 7'09 C. 0.KOE'CHL M16 W A? TORN 1 124). 16, 1937. Q Q KQECHLING 2,071,075

TELEPHONE S YS TEM Filed July 20, 1955 5 Sheets-Sheet 2 FIG. 3

//v I/E/V TOR C. D. KOECHL //V6 A T7'ORMEV Feb. 16, 1937.

C. D. KOECHLING TELEPHONE SYSTEM Filed July 20, 1955 FIG. 4

5 Shee lNVE/VTOR ts-Sheet 3 C. D. KOECHL ING ATTORNEY 16, 1937- c. D.KOEHUNG 011,075

TELEPHONE SYSTEM Filed July 20, 1955 5 Sheets-Sheet 4 FIG. 7 lNl 'NTORBy C. D. KOECHL/NG A T romwsr Feb. 16, 1937. Q 11 KOECHLING 2,071,075

TELEPHONE SYSTEM 7 Filed July 20, 1935 5 Sheets-Sheet 5 FIG. 6

C. D. KOECHL/NG waw AI TORNEV Patented Feb. 16, 1937 UNITED STATESPATENT OFFICE TELEPHONE SYSTEM Charles D. Koechling, Floral Park, N. Y.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of'New York Application July 20, 1935, Serial No. 32,312

11 Claims.

necting points of the switch. A system of this kind is disclosed inthepatent to L. R. Waller 1,567,309 of December 29, 1925. Systems havealso been provided in which, in addition to connections between twosubscribers lines over a link, connections may be established fromsubscribers lines to trunks. A system of this kind is disclosed in thepatent to E. E. Hinrichsen 1,567,054 of December 29, 1925.

A feature of the present invention is an arrangement, in a system inwhich connections are established between two subscribers lines in aswitch by means of links, whereby such subscribers lines may be arrangedin groups and in which means is responsive to the calling of a firstline in any of said groups for establishing a connection through an idlelink from the calling line to a second line in said group if said firstline is busy.

Another feature is an arrangement in a system of this kind in whichconnections may be established between a subscribers line and a trunk,whereby if a trunk has been called and connected to and a key. at thecalling subscribers station is actuated, a holding condition isestablished on this connected trunk so that the calling subscriber mayhang up his receiver and release his line from this trunk and wherebythe same or any other calling subscribers line may establish aconnection to the held trunk and remove the holding condition.

Another feature of this invention is an arrangement in which theestablishing of the connection from a calling subscriber to an idle linkis effected by the calling subscriber removing his receiver from theswitchhook and operating a key at his station and in which theestablishing of a connection to a trunk is effected by the callingsubscriber lifting his receiver from the switchhook and operating a keycorresponding to the particular trunk desired.

The invention has been illustrated in connection with the followingdrawings in which:

Fig. 1 shows diagrammatically how lines, links and trunks are arrangedon a cross-bar switch in a small capacity automatic telephone system;

Figs. 2 to 7 show the various features of the invention applied indetail to a small capacity automatic telephone system;

Fig. 2 shows a master station arranged to originate local and trunkcalls, to extend trunk calls w to another station which is ordinarilyarranged for local service only and to make trunk calls on an emergencybasis; a station arranged to originate local and trunk calls but withoutthe other features of the master station, and a station arranged to makeand receive local calls tion to the desired line and one trunk circuitin detail for extending calls to the central ofiice, While Fig. 7 showssignaling apparatus used in magneto areas.

Fig. 1 shows schematically the arrangement of the station lines, thelinks and the trunks on a cross-bar switch. The station lines appear onthe vertical units, a station such as 235 (Fig. 2) may appear onvertical unit IM and one such as 208 may appear on vertical unit I02.Three link circuits I 03, I04 and I05 appear on the six uppermosthorizontal levels and provide for three simultaneous inter-stationconnections. Three trunk circuits I05, I01 and I08 appear on the threenext lower levels to provide service from the stations to controlofiices. The lowermost horizontal level is not used in the systemdisclosed in the drawings but might be utilized for another trunkcircuit or for other purposes. By this arrangement the station appearingon vertical unit IOI can communicate with the station appearing onvertical unit I02 over link I03 by the operation of the contacts atcross-points I09 and I I0 and in a similar manner the station appearingon vertical unit I02 can originate or answer a call from the centraloiiice over trunk I06 by the operation of the contacts at crosspointIII.

The system as disclosed in Figs. 2 to 7 comprises an automatic system ofthe cross-bar type in which all the stations may communicate with eachother but only certain ones may make and receive calls over the trunks.The privileged stations are grouped into three classes, the first,exemplified by station 2M, is permitted to originate and receive callsover the trunks and in addition may be connected to any trunk which isin use to another station, the second, exemplified by station 298 whichmay originate and receive calls but does not have the privilege of beingconnected to a busy trunk and the third (not shown) which may receivebut may not originate trunk calls. The trunks are connected to theprivileged stations by means of keys individual to each trunk in such amanner that the station circuit is associated with the trunk circuit byoperating the key associated with the particular trunk desired. Holdkeys are also provided so that a call on any one of the trunks may beanswered at one of the stations having this service and held while thestation desired is dialed and the person who answers is instructed topick up the trunk call by operating the appropriate trunk key. Thisfeature makes possible the desirable arrangement of answering allincoming calls at the same point and extending them to the desiredstations.

In dial areas, outgoing calls to a central office are dialed in theusual manner and in manual common battery districts the call is passedver bally. In magneto areas additional equipment, shown schematically inFig. 7, is furnished in the trunk circuit which sup-plies talkingbattery to the station connected to it and signals the central officeautomatically.

Local calls are made from the key stations by operating the local keyand dialing in the usual manner. Stations having no trunk privileges arenot furnished with any keys but are provided with a dial for localcalls.

The operation of the system will now be described in detail.

Outgoing trunk: call Let it be assumed that the subscriber at'station 2Mshown in Fig. 2 desires to originate a call to a central ofiice. To dothis he removes the handset 289 from the cradle 29! and operates key 202which associates his handset with the first trunk to the central office.The removal of the handset and the consequent operation of the cradlecontacts cause the operation of line relay 40L The circuit for thisfunction is traced from ground through the upper back contacts and upperwinding of relay til i, upper outer back contacts of relay 492,right-hand middle back contacts of emergency key 2535, upper contacts ofthe switchhook springs associated with cradle Eel, pulsing contacts ofdial 263, the receiver of handset 200, left-hand winding of inductioncoil 2%, right-hand inner back contacts of key 2&5, upper inner backcontacts of relay 392 to battery through the lower winding of relay ldl.Relay 40L operated, disconnects the ground through its back contactstraced above and substitutes a ground through its upper front contacts.This ground is fed through a repeating coil (not shown) in the commoncircuit 55'? in order to give the subscriber busy tone in case all thelinks or the trunk selected are busy. In operating, relay 48! alsocloses its five lower front contacts which connect the subscriberstation to the common equipment.

It will be assumed that the first trunk (shown in detail in Fig. 6 andassociated with key 28.2)

has been selected and that this trunk is idle. A circuit is now closedfrom groun through resistance 585, contacts 55322 of relay the windingof relay 50 1, contacts 4% of relay til i, right-hand outer contacts ofkey 2%, middle switchhook contacts associated with cradle 2 5i, front citacts of key 292, lower inner contacts of relay to battery through thewinding of reiay Both relays 553i and Sci operate in this circuit. Theoperation of relay till causes the operation of select magnet AM in acircuit traced from ground through the contacts of relay 'l to batterythrough the Winding of select Select magnet 4&4, operated, moves thefingers of the select magnet bar into a position such that the cross-barwill be operated when the hold magnet operates and through its operatedcontacts energizes relay 5N3. Relay operates and causes the operation ofcut-oil relay tile in a circuit traced from ground through the lowerinner contacts of relay 5H3, lower contacts 1 relay 5335 to batterythrough the winding of cut-oil relay M5. Relay M35, operated, energizesthrough upper outer contacts, vertical magnet and through its lowercontacts connects ground. to the common conductor 4% to the stationsubset.

The operation of relay 52H also causes the operation of relay 585 in acircuit traced from ground through resistance Elle, contacts 5632 of:relay 533, upper front contacts of relay 58!, back contacts of relay 5%and the other relays similar to relay 5&5 associated with the otherstation circuits, upper inner back contacts of relay 561, upper innerback contacts of relay upper inner back contacts of relay 539 to batterythrough the Winding of relay 585. Relay 535, operated, energizes relay5% which operates and locks to ground through the lower outer contactsof relay 526. The operation of relay opens the operating circuits ofrelays 5%, 5&8, MS and the other similar relays associated with theother line circuits (not shown) releasing the one which was operatedwhich in this case was relay 5M. The release of relay 5M opens theoperating circuit and releases relay 5%.

The operation of vertical magnet lEiZ causes all the springs associatedwith bar to be operated and also opens the operatin path for line relaytill, releasing it. The release of relay l-fil opens the operating pathof relay till causing its release and the release of relay till opensthe operating path and releases select magnet .53 3, which in turnreleases relay Kilt which opens the locking circuit of relay 5G3releasing it. The cutoff relay M25 is now held operated through thecontacts of the switch. This circuit is traced from ground through thelower contacts of relay 4305, conductor tilt, right-hand outer contactsof key 235, the middle switchhook contacts associated with cradle 25!,front contacts of trunk key 202, contacts H5 associated with bar 5537 tobattery through the winding of cut-off relay Relay L lli holds magnet$532 operated and the springs associated with bar lii'l remain operatedafter select magnet 4M has been released in accordance with the usualmethod of operation of this type of switch. The tip; ring, hold and busyconductors in addition to the sleeve. conductor are also extendedthrough the switch. Ground on the busy conductor operates the busy relay532 in a circuit traced from ground through the upper inner contacts ofrelay 5%, contacts M5 associated with bar ll to battery through thewinding of relay M2. The operation of the latter relay opens at itsleft-hand contacts the incoming ringing bridge; removes the winding ofrelay 6M from conductor M3 to the keys of stations which do not have theprivilege of connection to busy trunks and connects this conductor tothe common tone circuit in common equipment 5% so that busy tone isreturned should the No. 1 trunk key be operated at any of these stationsand prepares the hold feature which will be described later.

The closure of the tip and ring conductors through the switch signalsthe central office over conductors E133 and 604 in the usual mannercausing an operator to be connected where this apparatus is located in amanual common battery area or causing dial tone to be returned in dialareas. When this equipment is located in a magneto central office area aspecial auxiliary apparatus shown schematically in Fig. 7 is interposedin conductors 541 and 548 to supply talking battery to the station lineand to signal the central ofilce automatically. The trunk circuit in theformer case is traced from central office trunk conductor 603, left-handouter back contacts of emergency key 205, conductor 548, lefthand backcontacts of relay 605, left-hand contacts associated with bar 401,right-hand middle back contacts of key 2.05, upper contacts associatedwith cradle 20!, pulsing contacts of dial 203, the receiver of handset200, left-hand winding of induction coil 204, right-hand inner contactsof key 205, the contacts next to the left associated with bar 401,conductor 541, left-hand inner back contacts of key 205 to trunkconductor GM to the central ofiice. Conversation with the central ofiiceoperator may now take place in case of a manual extension of theconnection and as the station apparatus 254 is shown as the localbattery type, talking battery is supplied from. battery 2% which isconnected in a local circuit including the lower contacts associatedwith cradle 2!, the transmitter of handset tail and the right-handwinding of induction coil 29 2. If the connection is to be extendedautomatically the moving of the dial 203 off normal short-circuits thereceiver of handset 2M in accordance with the standard practice for thistype of substation apparatus.

Where this equipment is located in a magneto central off ce area thetrunk circuit is the same that described above except that Fig. 7 isinterposed in the trunk circuit to the central office, relay operates,operating relay 152 momentarily which connects ringing current to trunkconductors H13 and 604 as the signal of an incoming call.

To release the connection the handset is replaced on the cradle. Thisopens the circuits through the switchhook contacts associated with thecradle, the upper set of contacts opening the line circuit, releasingthe central oflice equipment in manual common battery or dial offices inthe usual manner or signaling the central oilice to disconnect by meansof Fig. '7 in which the release of relay ltl causes the momentaryoperation of relay 152, connecting ringing current to the lineconductors in the case of a magneto office; the middle set of contactsopening the holding circuit of relay 4B5, releasing it and in turnreleasing magnet 362 which releases the switch and the lower set ofcontacts opening the local battery transmitter circuit. The release ofthe switch opens the circuit of the trunk busy relay 682 releasing itIncoming trunk call In a manual common battacts of key 285 to conductor884. In magneto areas, Fig. '7 is furnished and relay 15!! is operatedby the incoming ringing current, operating relay M3 and extending theringing current to relay l 5%! over the path traced above wheneverringing current is applied to conductors 603 and 504.

The operation of ringing relay 601 through its outer contacts causes theoperation of relay 609.

Relay i389, operated, locks in a circuit traced from.

battery through the winding and left-hand inner front contacts of relay639, right-hand middle back contacts of relay 602 to ground in thecommon tone, ringing alarm and timing circuit 606. The operation ofrelay 609 closes ground over conductor $55 to the common circuit 601which thereupon operates several audible signals (not shown) as anindication of an incoming call; connects battery through its right-handinner front contacts to the filament of trunk lampi 6 which lights andindicates the trunk on which the call has appeared; connects groundthrough its left-hand middle front contacts to conductor 645 whichoperates a relay (not shown) in the power supply circuit and increasesthe rate of charge of the battery for the duration of the call andthrough its left-hand outer contacts transfers conductor M2 from thebusy tone circuit to conductor tilt, so that restricted service stationsassociated with conductor 5B2 may'beeg connected to the trunk onincoming calls.

The subscriber at station 2M or at any other station where the audiblesignal and visible signal iiiil appear may answer the call by removthehandset from the cradle and operatingl.

the trunk key associated with lamp 6H]. This connects his telephoneinstrument to the trunk through. the cross-bar switch in the same manneras described previously for an outgoing call.

The association of one of the stations with the? trunk operates relay5&2 as before and the operation of relay 6&2 opens the locking circuitof relay 5% just described releasing the latter relay and extinguishingthe ringing signals. At the completion of the conversation the replacingof the;

handset on the cradle releases the line and trunk equipment as before.

Station-to-statz'on call To illustrate the operation of the circuit inmaking a station-to-station call it will be assumed that the subscriberat station 208 desires to communicate with the subscriber at station25%. To do this he removes handset 225 from cradle 232$, operates localkey 238 and dials the code of the desired line which in this case is 24.

As explained previously a station-to-station call is completed by meansof a link circuit one of which is shown in detail in Figs. 5 and 6. Thelinks are rotated in service in a manner to be described later and forthe purposes of illustration it will be assumed that the link shown isthe one to be used. The calling subscribers line is connected to thelink in much the same manner as that described previously for a trunkcall except that in this case a relay in the link is operated in serieswith the relay in the line circuit. Line relay 36! operates in a circuittraced from ground through the upper back contacts and upper winding ofrelay Siii, upper outer contacts of magnet 352, upper switchhookcontacts associated with cradle 226, pulsing contacts of dial 228, thetransmitter of handset 225, left-hand winding of induction coil 229,upper inner contacts of magnet 382 to battery through the lower windingof relay 35L The series circuit mentioned above now connects relays 552and &3 together to associate the calling end of the link with theparticular station line through the cross-points of the switch.

The circuit for this function is traced. from ground through resistance5%, back contacts 555 of relay 523, the winding of relay 513, lower nextto the outer contacts of relay 3M, middle switchhook contacts associatedwith cradle 226, the back contacts of keys 227i, 239 and 232 in series,operated contacts of key 25 lowermost contacts of relay start conductor529, upper back contacts of key 555, upper back contacts of relayleft-hand back contacts of relay 2 15, conductor 53 .3 to batterythrough the upper winding of relay 552. Both relays 5E2 and 513 operatein this circuit. The operation of relay 552 causes the operation ofselect magnet 1-58 in a circuit traced from ground through the lowerouter contacts of relay 512, back contacts 555 of relay EH5 to batterythrough the winding of select magnet 588. The operation of select magnet322 causes the operation of relay 5H3 as before and with relays 5E2 and513 both operated. a circuit is closed to operate relay 3% which in turnoperates magnet 552 releasing relay 3%! as previously described. Withselect magnet 458 and hold magnet both operated the contacts associatedwith bar are operated to connect the line circuit to the calling end ofthe link circuit. The operation of relay 5E3 also causes the operationof relays 555 and as previously explained.

Relay 5? 5 now operates in a circuit traced from ground through arepeating coil (not shown) in common circuit 5!? upper front contacts ofrelay 552, upper winding of relay 5E8, left-hand outermost contactsassociated with bar 325, uppermost contacts associated with cradle 226,pulsing contacts of dial 223, transmitter of handset left hand windingof induction coil 225, the contacts 2i? associated with bar 225 tobattery through the lower winding of relay 5E8. Relay iiiS, operated,closes a circuit through its front contacts to energize the winriirv ofrelay 525. Relay 555, operated, opens the circuit to select magnetreleasing it, prepares the pulsing circuit from the back contacts ofrelay 518,

connects ground to conductor 65 i to increase the charging rate of thebattery and puts ground on the off-normal conductors to be describedlater. The release of select magnet 558 releases relays 533 and 523 asbefore. Relay 512 now locks in a circuit traced from ground throughcontacts 5L9 of relay 5E5, upper inner back contacts of relay 522, upperinner back contacts of relay 521 to battery through the lower innercontacts and lower winding of relay 512. Relay 5E2 is of theslow-to-release type and does not release during the interval betweenthe opening of the circuit through its upper winding when relay 351releases and the closure or" the locking path through its lower windingjust described.

The line and link circuits are now in a condition for dialing, dial tonebeing furnished through the repeating coil in common circuit 511 throughthe upper front contacts of relay 5E2. The subscriber upon receivingdial tone will operate dial 228 in the usual manner, releasing andreoperating relay 518 in accordance with the number dialed which in thiscase has been assumed to be 24. When the dial is moved off normal thetransmitter of handset 225 is short-circuited and the receiver circuitis opened in the usual manner. The release of relay 518 on the firstdialing pulse causes the operation of relay 522 in a circuit traced fromground through the back contacts of relay 518, innermost contacts ofrelay 515, back contacts of relay 523, contacts of relay 524 to batterythrough the winding of relay 522. Relay 525 also operates on the firstpulse in a circuit traced from ground through the back contact of relay5%, innermost contacts of relay 515 to battery through the winding ofrelay 525. Relay 525 is of the slow-to-release type and does not releaseduring the momentary opening of this circuit during dialing. Theoperation of relay 522 causes the operation of relay 526. The circuitfor this operation is traced from ground through contacts 555 of relay5E5, upper inner back contacts of relay 525, inner contacts of relay525, upper front contacts of relay 522, lower outer backcontacts ofrelay 521, back contacts 521 of relay 525 to battery through the windingof relay 526. Relay 52E locks for the duration of the first train ofpulses through its make-before-break contacts in a circuit traced fromground through contacts 519 of relay 515, upper inner back contacts ofrelay 520, inner contacts of relay 525, to battery through the frontcontacts 52'! and winding of relay 525.

When relay 5M3 reoperates after the first pulse relay 522 is heldoperated and relay 523 is operated. Thus when relay 518 operates groundis removed from one side of the winding of relay 523 and it operates inseries with relay 522 holding the latter relay operated. This circuit istraced from ground through contacts 519 of relay 515, upper inner backcontacts of relay 52!), inner contacts of relay 525, upper winding ofrelay 523, lower contacts of relay 522, contacts of relay 525 to batterythrough the winding of relay 522. When relay 518 releases on the seconddial pulse relay 524 operates and holds relay 523 operated but releasesrelay 522. This circuit is traced from ground through the back contactsof relay 518, innermost contacts of relay 515, front contacts and lowerwinding of relay 523 to battery through the winding of relay 525. Relay522. released, causes the operation of relay 521 in a circuit tracedfrom ground through contacts 555 of relay 5S5, upper inner back contactsof relay inner contacts of relay 525, upper back contacts of relay 522,upper front contacts of relay 525 to battery through the upper innerback contacts and winding of relay 521. Relay 525 locks through itsmake-before-break contacts in a circuit traced from ground throughcontacts 5i9 of relay 515, upper inner back contacts of relay 525 tobattery through the upper inner front contacts and winding of relay 521.Upon the reoperation of relay 513 after the second dial pulse relays 523and 524 release.

t has been assumed that the number of pulses in the first digit is two.Had it been three, relay 522 would have operated again on the thirdpulse which would have caused the operation of relay 530. Should afourth pulse be dialed (for which there is no code assigned) relay 529will be operated when relay 522 releases. The operation of relay 523 atthis time would prevent connection to any station. At the end of thefirst train of pulses relay 525 releases, releasing relay 525.

When relay 5? releases on the first pulse of the second digit relays 522and 525 are operated as before. The operation of relay 525 causes theoperation of relay 53! in a circuit traced from ground through contacts.532 of relay 5l5, lower outer front contacts of relay 525, lower innerback contacts of relay 526, lower inner front contacts of relay 52! tobattery through the winding of relay 53! and resistance 533. Relay 53!looks in a circuit traced from ground through contacts 5!9 of relay 5l5,upper inner back contacts of relay 520 to battery through the upperinner front contacts and winding of relay 53! and resistance 533. Theoperation of relay 522 causes the operation of relay 6!! in a circuittraced from ground through contacts 5!!) of relay 5l5, upper inner backcontacts of relay 520, inner contacts of relay 525, upper front contactsof relay 522, lower outer front contacts of relay 52!, back contacts 528of relay 526, upper outer back contacts of relay 5 l8, upper middle backcontacts of relay EH9, upper outer back contacts of relay 620, upperouter back contacts of relay 62! to battery through the upper inner backcontacts and winding of relay H. Relay 6!! locks in a circuit tracedfrom ground through contacts E9 of relay 5l5, upper inner back contactsof relay 520, upper inner back contacts of relay M9, upper inner backcontacts of relay BIB, upper inner back contacts of relay 62!, upperinner back contacts of relay 620 to battery through the upper innerfront contacts and winding of relay 6.

Relays 52c, 62! and Gill now successively operate on the back and frontcontacts of relay 522 under control of pulse relay 5!!! over the pathsalready traced. Each relay operates through its own back contacts andlocks through its make before break contacts, opening the locking pathand releasing the preceding relay. I-Iad five pulses been dialed, relayElli wouldhave been operated and relay M3 released. If six had beendialed, relay 522 would have been operated but in this case relay M3 isnot released. If more than six pulses had been dialed, relays 6H, 62!),62! and (H8 would have operated a second time in the same manner asdescribed previously depending on the digit dialed and the operation ofeach of these relays would have released the previous relay as explainedbefore.

At the completion of the second train of pulses, relay 525 releases andcauses the operation of relay 529. This circuit is traced from groundthrough contacts 532 of relay 5!5, lower outer back contacts of relay525, upper outer front contacts of relay 53f to battery through therighthand inner back contacts and winding of relay 529. Relay 529 locksoperated in a circuit traced from ground through contacts 5H3 of relay5!,5, upper inner back contacts of relay 523 to battery through theright-hand inner front contacts and winding of relay 5129. Relay 525 nowoperates in a circuit traced from ground through contacts 559 of relay5l5, upper inner back contacts of relay 523, right-hand next to theinner front contacts of relay 523 to battery through the winding ofrelay 525.

A busy test is now made by the connection of busy test relay 534 to thesleeve of the called subscribers line, ground on the latter indicating abusy condition. The busy test circuit is traced from battery through thewinding and lower inner backcontacts of busy test relay 534, frontcontacts 535 of relay 53E, left-hand inner front contacts of relay 529,right-hand outer back contacts of relay 530, lower outer back contactsof relay 522, lower outer front contacts of relay M8, to the sleeveconductor of station line 2M, with which sleeve relay 405 is associated.If this line is busy, the sleeve conductor is connected to ground asexplained previously and busy test relay 53 i operates, opens thecircuit to relay 509 to prevent connection to the line and connects busytone through condenser 535 to the line. If ground is not present on thesleeve of the line circuit relay does not operate and relay 509 operatesin a circuit trace-d from ground through resistance 5H3, contacts 53'!associated with relay 533, lower outer front contacts of relay 526,lower outer front contacts of relay 53!, upper back contacts of relay534 to battery through the winding of relay 539. The operation of relay509 closes a circuit for the operation of select magnet 309. Thiscircuit is traced from ground through contacts 5!!! of relay 5l5, upperinner back contacts of relay 523, lower outer back contacts of relay538, upper outer front contacts of relay 5% to battery through thewinding of select magnet 539. The operation of relay 509 also causes theoperation of relay 535 in a circuit traced from ground throughresistance 5M, contacts 53'! of relay 533, upper inner front contacts ofrelay 509 to battery through the winding of relay 535. The operation ofselect magnet 439 causes the operation of relay 5|0 by connecting groundto its winding terminal and the operation of relay 535 causes theoperation of relay 503. Relay 5H! operated, provides a locking path forrelay 533 and short-circuits relay 53!, causing it to release. The pathover which ground is connected to the right-hand winding terminal ofrelay 53! has already been described and the path over which ground isconnected to the left-hand winding terminal is traced from groundthrough the lower inner front contacts of relay 5l0, lower inner frontcontacts of relay 509 to the lefthand winding terminal of relay 53!. Therelease of relay 53! causes the operation of cut-off relay 335 in acircuit traced from ground through contacts 5! 3 of relay 5l5, backcontacts 535 of relay 53!, left-hand inner front contacts of relay 529,right-hand outer back contacts of relay 530, lower outer back contactsof relay 622, lower outer front contacts of relay 6l8 to battery throughthe winding of cut-off relay 405. The latter relay operated, operateshold magnet 402 which with the simultaneous operation of select magnet409 causes the operation of all of the contacts associated with bar M0in the usual manner.

The operation of the contacts associated with bar M0 closes through thewanted subscribers line to the terminating end of the link circuit andoperates relay 538. The circuit for the latter function is traced fromground through the upper inner front contact of relay 435, contacts 4,upper outer back contacts of relay 520 to battery, through the windingof relay 538. The operation of relay 533 opens the operating circuit ofselect magnet 409, releasing it which opens the operating circuit ofrelay 5H3 releasing it and releasing relay 503 in turn. The operation ofrelay 538 also connects ringing current through ringing trip relay 539to the tip and ring conductors of the through the upper winding of relay539. operation of relay 539 disconnects the ringing wanted subscribersline while an audible ringing signal is connected to the tip and ringconductors of the calling subscribers line. The ringing circuit istraced from the ringing current supply from the common circuit 511, overconductor 54B, lower inner back contacts of relay 539, upper middlefront contacts of relay 538,1eft-hand contacts associated with bar 410,right-hand middle back contacts of key 255, condenser 295, ringer 291,right-hand inner back contacts of key 295, cont-acts !.'1 associatedwith bar M9, upper inner front contacts of relay 538, upper middle frontcontacts of relay 521, lower outer back contacts and lower Winding ofrelay 539, conductor 541 to the ringing supply in common circuit 511.The audible ringing tone path is traced from the common circuit 51'!over conductor 549, through the lower inner front contacts of relay 538,upper outer front contacts of relay 521, condenser 542, condenser 536,to the tip conductor of the calling subscribers line.

When the subscriber at the called station 214 answers by removing thehandset from the cradle and operating key 23 1, ringing trip relay 539operates in the usual manner and locks in a circuit traced from groundthrough contacts 532 of relay 5i5, upper front contacts of relay 539,lower back contacts of relay 529 to battery The current from the calledline. Relay 525 now operates through the contacts of key 23! in acircuit traced from ground through the lower contacts of relay 405,right-hand outer back contacts of key 295, middle contacts associatedwith cradle 291, back contacts of keys 292, 299 and 219 in series,operated contacts of key 208, righthand contacts associated with bar 413to battery through the winding of relay 529. Relay 525 remains operatedin the circuit just described for the duration of the call and, inoperating, opens the operating circuits and releases relays 538, 539,526, 521, 529 and 618. Cut-off relay 405 is now held operated undercontrol of relay 525 in a circuit traced from ground through contacts519 of relay 515, the upper inner front contacts of relay 520, contacts418 associated with bar 410, to battery through the winding of relay405. The tip conductor of the calling subscribers line and the ringconductor of the called subscribers line are connected together throughcondenser 536 and the upper inner back contact of relay 538 for thetransmission of speech and the ring of the calling line and the tip ofthe called line are connected together through condenser 543 and theupper middle back contacts of relay 538. Talking battery is supplied tothe calling subscriber through the windings of relay 518 and to thecalled subscriber through the windings of retard coil 544.

Upon the completion of the conversation, both subscribers replace thehandsets on the cradles. In the case of the calling subscriber thisopens the operating circuit of relay 518, releasing it, in turn openingthe operating circuit and releasing relay 515. The operating circuit ofrelay 393 is also opened at the middle contacts associated with cradle223 and relay 353 releases, releasing hold magnet 392. Cross-bar 394 nowreturns to its unoperated position releasing the contacts associatedwith it. The replacing of the handset on the cradle at the calledsubscribers station, opens the operating path of relay 525 through themiddle contacts associated with cradle 201, releasing this relay. Therelease of relay 520 removes ground through its'upper inner frontcontacts from the sleeve conductor of the called line, releasing cut-offrelay 405. The release of the latter relay opens the operating circuitof hold magnet 492, releasing it and permitting cross-bar 419 to returnto its normal position. Both calling and called lines are now in theiroriginal or idle condition.

Line hunting The system is arranged to provide line hunting facilitiesfor some of the lines. This is illustrated in the drawings by theassociation of lines 25 and 21 in one group and lines 35 and 3? inanother group in such a way that if, for example, line 25 is dialed andis found to be busy, the connection is automatically extended to line21, or, if line 35 is dialed and found to be busy, the connection isautomatically extended to line 31. This is done by substituting relay611 for busy test relay 534 in case line 25 or 36 is dialed.

It will be assumed that station 21 1 whose code is 25 has been called.The operation of the circuit under this condition is the same aspreviously described until the completion of the dialing of the seconddigit. At this time, a circuit is closed from the sleeve conductor ofthe wanted station line to relay 511. This circuit is traced from theleft-hand winding terminal of cut-off relay 413, which may or may nothave ground connected to it, through the right-hand outer back contactsof key 212, lower next to the outer contacts of relay B19, lower next tothe inner contacts of relay 922, right-hand inner back contacts of relay529, left-hand middle front contacts of relay 529, lower inner frontcontacts of relay 531 to battery through the upper inner back contactsand winding of relay 611. If station 211 is busy, ground will be presenton the sleeve conductor and relay 917 will be operated. Relay B17operated, locks and connects the sleeve of line 2'! to the terminatingend of the link in the same way as if 7 had been dialed as. the seconddigit. Busy test relay 535 is now connected to the sleeve of line 2! andthe regular busy test is made on that line as previously described. Ifthe sleeve of line 25 had not been grounded, relay 61'! would not haveoperated and with relays 611 and 534 both non-operated, the terminatingend of the link would have been connected to line 26 in the line to linecall as described previously.

Calls from and to keyless stations When a keyless station 235 originatesa local call, the operation of the circuit is similar in every respectto that just described for key station operation except that theoperation of line relay 309 causes the operation of relay 512 directlyinstead of through the switchhook contacts and the local key aspreviously described. Also relay 33'! is held operated by relay 515through the contacts of the switch. This circuit is traced from groundthrough contacts 532 of relay 515, contacts 359 associated with crossbar355 to battery through the winding of cut-off relay 301.

If the keyless station 235 is called, the operation of the circuit isthe same as that described for a key station with the exception thatrelay 535 when it operates, due to the removal of the handset from thecradle, connects ground through the cross-points of the switch tooperate relay 529. This circuit is traced from ground through contacts522 of relay 515, upper contacts of relay 539, cross-bar contacts 319,crossbar contacts 3 to battery through the winding of relay 520.

Station 2H is also a keyless station and is normally connected tokeyless station equipment M2, 453 and 4M through the inner back contactsof transfer key 292. With key 2H? in the normal position, as shown,station 2! i may originate and receive calls like other keylessstations. It is arranged, however to receive trunk calls extendedthrough the master station 2M as will be described later.

Trunk holding The system is arranged so that incoming calls from thecentral ofiice may be answered at one or more stations and held whilethe desired station is called locally and informed of the call. Byoperating the trunk key associated with the incoming call the wantedstation is connected to the trunk and the holding condition is removed.

To illustrate this arrangement it will be assumed that an incoming callon trunk l shown in Fig. 6, has been answered by the attendant atstation Zi l, shown in Fig. 2, and it has been ascertained that station2&8 is wanted. The attendant at station 2M thereupon operates hold key243 momentarily. The operation of this key releases trunk key 202mechanically and causes the operation of relay $95 in a circuit tracedfrom ground through the lower contacts of relay @835, right-hand outercontacts of key 285, middle contacts associated with cradle 20!,contacts of hold key M3, contacts 499 associated with cross-bar Ml! tobattery through the wind ing of relay 6B5. Relay 6G5, operated, locksthrough its right-hand inner contacts to ground through contacts 623 ofrelay Gilt. The operation of relay 695 opens the central office trunk tostation 214 and connects the winding of relay. 62A in series withresistance 626 across trunk conductors 6M and 634 to hold the connectionto the central oflice. The winding of relay 62A is normallyshort-circuited by the right-hand outer back contacts of relay 505 andthe righthand inner front contacts of relay 5&2. This short circuit isremoved however, by the operation of relay 605 and relay 62 operates inthe trunk circuit. The operation of relay 625 causes the operation ofrelay 625. Relay 525, operated, prepared a holding circuit for relay 524to be described later and connects ground to conductor 6| I to increasethe charging rate of the battery. The release of key 202 opens theoperating cir" cuit, releasing relay 505 which in turn releases holdmagnet 432 and cross-bar dill. When this occurs the circuit to relay 662is opened and relay 602 releases. Relay 602, released, opens the lockingcircuit of relay 685 which releases. With relays 602 and 699 releasedand relay E25 operated the winding of relay 6M is connected to conductorBIZ so that stations having restricted service may pick up the call andrelay 625 is held operated and acts as the holding bridge, the lattercircuit being traced from trunk conductor 603, left-hand outer backcontacts of key 285, left-hand contacts of relay 625, the winding ofrelay 624, resistance 52%, left-hand inner back contacts of key 265 totrunk conductor BM.

Station 2M may now make a local call to the wanted station in the mannerdescribed previ ously by operating local key 231 and dialing the numberof the wanted station on dial 263. It will be assumed that the wantedstation is station 208.

When the attendant at station 208- has answered and has been informedthat a call from the central oilice is to be picked up on trunk #I heoperates key 221. The operation of this key mechanically releases key230 which was operated when he answered, releasing his line from thelink circuit as previously described. The operation of key 22? nowcauses the operation of relay 80! in a circuit traced from groundthrough resistance 5| 4, contacts 555 of relay 5513, the Winding ofrelay 5l3, the lower and next to the outer contacts of relay 3!. middlecontacts associated with cradle 226, front contacts of key 2271, lowerinner contacts of relay 38E, right-hand outer back contacts of relay 662to battery through the winding of relay sea. The operation of relay 6Massociates station 268 with the trunk circuit as previously described.When relay 6622 again operates through the cross points of the switch itshort-circuits relay 624. This short-circuiting path is traced from theleft-hand winding terminal of relay E24, right-hand outer back contactsof relay 605, right-hand inner front contacts of relay 602 to theright-hand winding terminals of relay 624. Relay 624, released, opensthe operating circuit of relay 625 releasing it. The trunk circuit isnow connected in the usual way to station 208 under control of theswitchhook contacts and keys of this station.

Extension of trunk calls to two wire stations The system is arranged toextend trunk calls to one or more two wire stations by means of keyslocated at the master station. In the drawings two wire station 21 l isso arranged by means ofv keys 2I5, M2 and BIG located at master station2M. With these keys in their normal position the line wires of station2!! are connected through the right inner and left inner back contactsof key M2 to line relay H2 which permits station 2H to make and receivelocal calls in the manner described previously. If it is desired toextend a trunk call which has been connected to station 2H4 to station 2the attendant at station 2M first operates key 2l5 which connects theline wires of stations 2M and 2 together through condensers 2|! and H8and permits him to monitor on station 2!! to ascertain whether or notthe station is busy. Having determined that station 2!! is not busy key2l2 is next operated. The operation of key 2l2: connects the line wiresof station 2H to the line wires of station 2M through the left-handfront contacts and right-hand inner front contacts of key 2l2 and therightand left-hand back contacts of key 255; through its right-handmiddle front contacts connects a shunt across the middle switchhookcontacts associated with cradle 28! to permit station 2M to replace thehandset on the cradle without releasing the connection; connects groundthrough its right-hand outer front contacts to the sleeve conductor ofthe line equipment associated with station 2 so that this line will testbusy to incoming calls and through its right-hand outer back contactsdisconnects the cut-off relay 4H3 so that the latter relay and holdmagnet M4 will not operate falsely. The bell at station HI may now beoperated by operating key 2H5 momentarily, the line circuit being openedat the back contacts of key M6 and ringing current from the commandment2l9 being applied to the line conductors to station 2!! through thefront contacts of key 2l6. After station 2H has answered station 2M maymonitor on the conversation or replace the handset on the cradle asdesired. At

the termination of the conversation key M2 is returned to its normalposition.

Rotation of links In order that the links may receive equal wear anarrangement is provided to rotate them in service, that is to preselectthem so that they are used in rotation, the first link being used nextafter the last is reached. Facilities are shown in Fig. 6 to accomplishthis for three links.

When the first link (shown in detail in Fig. 51'

has been used, which condition is indicated by the operation of relaytie, ground through contacts 532 is connected over conductor 628, tobattery through the winding of relay BEE. Relay 6H3 operates, locksmechanically and transfers the start conductor 629 from conductor 635 toconductor 63% which is connected to the start relay in the second linksimilar to relay M2. The start circuit is then traced from ground onstart conductor 829, upper back contacts of key 6M, upper back contactsof relay 6H5, left-hand front contacts of relay G56, upper back contactsof key 635, upper back contacts of relay 53B, left-hand back contacts ofrelay 62? to conductor e 3! which is connected to battery through thewinding of the start relay, similar to relay 512 in the second link.

When the second link is used ground is connected to conductor 932 fromthe relay similar to relay 595 in the second link, operating relay 52'!which locks mechanically and transfers start cenductor 629 through theleft-hand front contacts of relay 52'! and the upper back contacts ofkey 63?, the upper back contacts of relay E338 and the left-hand backcontacts of relay ass to conductor 533 which is connected to the startrelay similar to relay 552 in the third link. When the third link isused ground is connected to conductor E34 and relay 83% operated. Withrelays SL, 62'. and 639 operated a circuit is closed from ground throughthe right-hand contacts of relay Bit, conductor right-hand contacts ofrelay 82'? and right-hand contacts of relay 538 to battery through thewinding of relay 5%. Relay Eflil operates in this circuit and connectsground to the winding of relay B ll operating the latter. Relay t ll,operated, connects ground to the windings of release magnets 6 52 and643 operating them and removing the mechanical locks from relays Bit and52?. If links No. i or No. 2 or both are still in use at the time linkNo. 3 is seized ground will still be present on conductors 628 or 632 orboth and relays sit or 62'! or both will continue in an operatedcondition. With relays 655, 62? and E39 operated a new call which isevidenced by ground on start lead 62% returns busy tone to the callingsubscriber by transferring the ground on conductor 629 through the upperback contacts of key tic, upper back contacts of relay 6E5, left-handfront contacts of relay 6 46, upper back contact of key 635, upper backcontacts of relay 335, left-hand front contacts of relay 62?, upper backcontacts of key 63?, upper back contacts of relay 538, left-hand frontcontacts of relay 639 to battery through the winding of a relay (notshown) in the common circuit 645 over conductor M l.

If either link No. l or No. 2 or both are idle relays 816, 62? or bothrelease when release magnets M2 and i343 operate. In this case the linkbusy path just traced is opened at either relay BIB or Ell as well asthe operating path of relay 5A0 releasing relay 85-1 and release magnets642 and 66-3 and one of the links will be used on the next call aspreviously explained. When the call which used link No. 3 is endedground is removed from conductor 834, releasing relay 839.

Facilities are provided so that any of the links may be convenientlywithdrawn from service for repair or other reasons. Thus the operationof key ti l transfers conductor $24 to the second link and places groundon conductor 646 in effect as if relay tit were operated. Similarlylinks No. 2 or No. 3 may be Withdrawn from service by operating key 635or 53?. Relays 5E5, 636 and $38 are provided so that the linksassociated with them will be automatically withdrawn from service incase the battery fuse associated with the individual link operates. Thisfuse is located in the common timing circuit 6% and when it operatesconnects battery to conductors 6 11, M3 or Gels depending on which linkis in trouble. Battery on conductor Ml operates relay 6l5 whichtransfers the start conductor 629 to the second link and groundsconductor 646. The operation of relays $31 or 638 perform similarfunctions for the second and third links. When relay 5l5, 635 or 63%operates due to an operated fuse battery is returned to common circuit655 over conductor 65% for alarm purposes.

Emergency service to the central office Arrangements for service to thecentral oflice on an emergency basis are provided to take care of thepossible condition where for any reason no calls can be made through theswitch. This is accomplished by the use of emergency switch 265 whichwhen operated disconnects master station sit from the station relayequipment and connects it directly to the first trunk to the centralcffice. With key 2535 operated station 25% may originate and receivecalls in the usual manner. Station 2M has been shown with equipmentarranged for magneto operation, a local talking battery 22d andsignalling generator 22! being furnished.

What is claimed is:

i. In a telephone system, a switch, subscribers lines terminating insaid switch, links terminating in said switch, means for establishing aconnection from any one of said lines to any particular other one ofsaid lines through a link, and means responsive to the calling of aparticular line for establishing a connection through a link from thecalling line to another line if said particular line is busy.

2. In a telephone system, a switch, groups of subscribers linesterminating in said switch, links terminating in said switch, means forestablishing a connection from any one of the lines in any one of saidgroups of lines to any particular line in any one of said groups througha link, and means responsive to the calling of a certain line in any oneof said groups for establishing a connection through a link from thecalling line to another line in the group of lines in which said certaincalled line is located if said called line is busy.

3. In a telephone system, a cross-bar switch, subscribers linesterminating in said switch, some of said lines arranged in pairs, linksterminating in said switch, means for establishing a connection from anyone of said lines to any particular other one of said lines through anidle link, and means responsive to the calling of a particular line of apair of lines for establishing a connection through an idle link fromthe calling line to the other line of said pair if said particularlycalled line is busy.

4. In a telephone system, a cross-bar switch, subscribers linesterminating in said switch, links terminating in said switch, means forestablishing a connection from any one of said lines to any one of theother lines terminating in said switch through an idle link, means forestablishing a connection from any one of said lines to a particular oneof said lines through an idle link, and means operated if saidparticularly called line is busy for establishing instead a connectionto another line through said idle link.

5. In a telephone system, a cross-bar switch, subscribers lines arrangedvertically in said switch, links arranged horizontally in said switch,trunks arranged horizontally in said switch, means for establishing aconnection from any calling line to any other line through a link, a keyat each subscribers station for each trunk, and means operated by acalling subscriber removing his receiver from the switchhook andactuating a trunk key for establishing a connection from said callingsubscriber's line to a corresponding trunk.

6. In a telephone system, a cross-bar switch, subscribers linesterminating in said switch, links terminating in said switch, means forestablishing a connection from a calling line to any other line throughan idle link, a relay associated with each line, means for operating therelay associated with the line when said line is busy, means responsiveto the calling of a first line in a certain group of lines if said firstline is busy and the associated relay is operated for establishing aconnection through an idle link from the calling line to a second linein said group. i

'7. In a telephone system, a cross-bar switch, lines terminating in saidswitch, links terminating in said switch having a calling branch and acalled branch, means for establishing a connection from a calling linethrough the calling branch of an idle link, means thereafter responsiveto digits represented by series of selective impulses incoming over theline for extending the connection through the associated called branchof said link to any line corresponding to the particular digitsselected, a cut-off relay associated with each line, means for operatingthe relay associated with a line when said line is busy, means operativeafter the digits representing a first line in a certain group of lineshave been received for preventing the extension of the connection tosaid first line if the associated cut-off relay is operated and forextending the connection to a second line in said certain group.

8. In a telephone system, a cross-bar switch, subscribers lines arrangedvertically on said switch, links arranged horizontally on said switch,trunks arranged horizontally on said switch, means for establishing aconnection from any calling line to any other line through an idle link,a key at each subscribers station for each trunk, a trunk holding key ateach subscribers station, means operative by a calling subscriberremoving his receiver from the switchhook and actuating a trunk key forestablishing a connection from said calling subscribers line to thecorresponding trunk, means thereafter responsive on the operation of thecalling subscribers trunk holding key for establishing a holdingcondition on the engaged trunk, means for releasing said callingsubscribers line from said trunk, and means thereafter operative inresponse to the establishing of a connection from any subscribers lineto said held trunk for removing said holding condition.

9. In a telephone system, a cross-bar switch, subscribers linesterminating in said switch, trunks terminating in said switch, a key ateach subscribers station for each trunk, a trunk holding key at eachsubscribers station, means operative by a calling subscriber removinghis receiver from the switchhook and operating a trunk key forestablishing a connection between said subscribers line and thecorresponding trunk, means thereafter responsive to the operation of thecalling subscribers trunk holding key for establishing a holdingcondition on the engaged trunk, means thereafter operative by thecalling subscriber replacing his receiver on the switchhook forreleasing his line'from said trunk, and means thereafter operative inresponse to the establishing of a connection from any callingsubscriber's line to said held trunk for removing said holdingcondition.

10. In a telephone system, a cross-bar switch, subscribers linesterminating in said switch, links terminating in said switch, a key ateach subscribers station, trunks terminating in said switch, a key ateach subscribers station for each trunk, means responsive to a callingsubscriber removing his receiver from the switchhook and operating saidfirst-mentioned key for establishing a connection between said callingsubscribers line and a link, and means responsive to a callingsubscriber removing his receiver from the switchhook and operating atrunk key for establishing a connection from said last-mentioned callingsubscribers line to a corresponding trunk.

11. In a telephone system, a cross-bar switch,

subscribers lines terminating in said switch, links terminating in saidswitch, a key at each subscribers station, trunks terminating in saidswitch, a key at each subscribers station for each trunk, meansresponsive to a calling subscriber removing his receiver from theswitchhook and operating said first-mentioned key for establishing aconnection between said calling subscribers line and a link, meansresponsive to digits represented by series of impulses transmitted fromsaid calling subscribers station over the connected link for connectingthe seized link to a called subscribers line corresponding to the digitstrans mitted, and means responsive to a calling subscriber removing hisreceiver from the switchhook and operating a trunk key for establishinga connection from said last-mentioned calling subscribers line to acorresponding trunk.

CHARLES D. KOECHLING.

